Before Quazi Mohammad Rezwanul Ahsan Nafis, a 21-year-old from Bangladesh, allegedly made plans with an FBI informant to blow up the New York Federal Reserve Bank, he sought guidance on his obligations under Islamic law, according to a criminal complaint.

Mr. Nafis had conversations on Facebook with the informant and another person, identified in the complaint only as a co-conspirator.

“The three discussed certain Islamic legal rulings that advise that it is unlawful for a person who enters a country with a visa to wage jihad there,” the complaint says. Mr. Nafis told his confidants that he had sought the advice of someone in his native Bangladesh, who said he wasn’t bound by such rulings.

“Accordingly, Nafis indicated that he believed that he was free to continue with his plan to conduct a terrorist attack on U.S. soil,” the complaint says.

We asked University of Washington law professor Clark Lombardi, an expert on Islamic law, about the rulings discussed in the alleged Facebook exchange.

First, he said, they are more accurately described as legal opinions by Islamic scholars. Mr. Lombardi said such opinions are scattered; some are published in newspapers, some are found in books, some are online and still others are passed on through word of mouth.

Offhand, he knew of none that discuss how visas might bear on jihad, and he emphasized that most Muslims would assume at the outset that, visa or no, terrorism “would put their soul in jeopardy.”

The opinions in question could prohibit a Muslim who asks for and is granted permission to enter a sovereign country from attacking his host, Mr. Lombardi said. In any event, Mr. Lombardi said he wasn’t surprised the alleged Facebook conversation took place.

“A Muslim would try to think about all the possible angles that weigh on the morality” of an action, he said. “The fate of their soul for eternity depends on them getting the answer right.”

Mr. Nafis was arrested Wednesday morning after he allegedly attempted to detonate what he thought was a 1,000-pound bomb inside a van parked at the New York Federal Reserve on Liberty Street.

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